The proposed research is an investigation of DNA packaging in Mitochrondria from normal adult and regenerating rat liver. In the first phase of the project, mitochondria will be radioactively labeled in vitro, and the membrane-bound DNA will be isolated as a Mg ion with respect to its size, circularity, strandedness, and its preferential attachment to membrane at specific base sequences. We will explore the possibility that a particular stage in the replication of mitochondrial DNA occurs concomitantly with the binding of the corresponding replicative intermediate to the membrane, and will also examine which membrane components appear to be directly involved in DNA binding. In the second phase of this work, procedures previously used in bacterial systems will be adapted for use in isolating a mitochondrial DNA complex in which the DNA remains folded in a compact structure. The macromolecular species that are present in the complex as well as other factors that stabilize the folded conformation will be studied. The DNA in the complex will be purified and analyzed in sedimentation velocity experiments and in Cs Cl ethidium bromide gradients to determine which kinds of replicating DNA molecules can exist in the folded conformation. By calculating the mass of the DNA in the folded structure from its sedimentation coefficient, we hope to determine if several microns 5 DNA circles co-exist in an single folded complex. The long range goal of this work is to elucidate mechanisms that control organelle biogenesis at the ultrastructural level of microchrondrial DNA.